1. Field of the Invention
The present invention relates to a humidification system for a fuel cell. More specifically, the present invention relates to a humidification system provided with a fuel cell which has been adapted as an energy source for a vehicle, such as an electric vehicle.
2. Description of Related Art
Recently, a vehicle, such as an electric vehicle, which utilizes a xe2x80x9cclean energyxe2x80x9d, such as a solid polymer type fuel cell, has been developed. The Japanese Unexamined Patent Application, First Publication No. 6-132038, for instance, discloses a solid polymer electrolyte type fuel cell which may be used for such an energy source.
In general, a solid polymer type fuel cell that is used for such vehicles has a laminate structure in which a power generating element is supported by gas separating members from both sides thereof. In the laminate structure, a plurality of gas passageways for supplying a reaction gas is formed on a power generating element which is formed by a hydrogen ion conductive solid polymer being sandwiched by a pair of carbon electrodes carrying platinum catalyst (i.e., a solid polymer electrolyte membranexe2x80x94electrode joined unit) and each electrode surface.
When the above-mentioned solid polymer type fuel cell is used, hydrogen gas is supplied to one of the electrodes as a fuel supply gas and oxygen or air is supplied to the other electrode as a supply gas for an oxidizing agent. In such a manner, electricity is extracted directly from chemical energy obtained by an oxidation reduction reaction of the fuel supply gas.
That is, the electric energy is taken out of the series of electrochemical reactions in which the hydrogen gas is ionized at the anode side to move in the solid polymer electrolyte and the electrons are moved toward the cathode side via an external load to react with the oxygen to produce water.
In the above-mentioned fuel cell, if the solid polymer electrolyte membrane is dried out, the efficiency in the ion conductivity thereof is decreased. Accordingly, the efficiency in the energy conversion is also decreased. Therefore, it is necessary to supply water to the solid polymer electrolyte membrane so that an excellent ion conductivity thereof may be maintained.
For this reason, a humidification device is provided with a fuel cell of the above type, which is capable of humidifying supply gas, such as a fuel supply gas and a supply gas for an oxidizing agent, and supplying water to the solid polymer electrolyte membrane so that an excellent reaction of at the membrane may be maintained.
The structure of an example of the humidification device will be explained with reference to FIG. 10. In FIG. 10, a humidification device is indicated by a numeral 1. In the humidification device 1, outside air which is pressurized by a super charger 2 is supplied to a supply gas line 5 as a supply gas for an oxidizing agent and the supply gas is humidified by the humidification device 1. The humidified air is then supplied to a fuel cell (hereinafter referred to as a stack) 3 and the oxygen contained in the humidified air is used as an oxidizing agent. After that, the gas is emitted as a discharge gas.
Also, the discharge gas containing water which is generated when reacted in the stack 3 is supplied to the humidification device 1, via a discharge gas line 6, from the stack 3. The water vapor contained in the discharge gas is transferred to the supply gas in the humidification device 1 and then evacuated.
As shown in FIG. 4, a pressure regulating valve 4 which regulates the inner pressure of the stack 3 is provided with the discharge gas line 6.
A humidifier 11 as shown in FIGS. 11 and 12 is disposed in the humidification device 1.
The humidifier 11 is formed by a plurality of tube type porous hollow thread members 12 which are made of a vapor permeable membrane (i.e., a water permeable membrane). The plurality of tube type porous hollow thread members 12 are contained in a cylidrically shaped casing 14 which has a plurality of opening portions 13 formed around its peripheral surface in the proximity to both ends thereof. The outer surfaces of the hollow thread members 12 as well as the outer surface of the hollow thread member 12 and the inner surface of the casing 14 are sealed at both ends of the casing 14.
In the humidifier 11, the supply gas is supplied from the opening portions 13 located in the proximity to one of the two ends of the casing 14. The supply gas is passed through the gap present between each of the hollow thread members 12 and exited from the opening portions 13 located in the proximity to the other end of the casing 14. Also, the discharge gas supplied from the stack 3 is supplied to the hollow thread members 12 from one end of the casing and exited from the other end.
As shown in FIG. 13, the hollow thread member 12 has numerous capillary portions 15 and the vapor contained in the discharge gas, which is introduced to the hollow thread members 12, is condensed in the capillary portions 15 and moved toward an outer periphery side thereof. The condensed vapor is then evaporated into the supply gas.
That is, the water content of the discharge gas is transferred to the supply gas in the humidifier 11 so that the humidification of the supplied gas is performed.
However, since extremely thin threads having an inner diameter of, for instance, about 0.3 mm (cf. the capillary portion size is about 4 nm) are used as the hollow thread members 12 in the humidifier 11, there is a danger that the capillaries of the hollow thread members 12 may be blocked by dust contained in the discharge gas which is supplied from the stack 3. Also, since the hollow thread members 12 used in the humidifier 11 are bundled and the supply gas is passed through between each of the hollow thread members 12, there is a danger that the gap between each of the hollow thread members 12 may also be blocked by dust which may be contained in the supply gas.
If the capillaries of the hollow thread members 12 or the gap between each of the hollow thread members 12 is blocked, a transfer of the vapor contained in the discharge gas to the supply gas cannot be satisfactorily carried out and, hence, a sufficient amount of water cannot be supplied to the stack 3. Thus, the efficiency in power generation of the stack 3 is decreased and this may lead to a cause of the failure of the stack 3.
Accordingly, one of the objectives of the present invention is to provide a humidification system for a fuel cell which does not have the above-mentioned problems.
Another objective of the present invention is to provide a humidification system for a fuel cell which is capable of quickly detecting a clogging in a humidifier so that the affect to a stack caused by the decrease in humidification of a supply gas due to the clogging in the humidifier may be suppressed to a minimal level.
The above objectives may be achieved by a humidification system for a fuel cell according to the present invention, including: a humidifier having a bundled plurality of tube type hollow thread members made of a water-permeable membrane, the humidifier transferring a water content contained in a discharge gas, which is emitted from a fuel cell, to a supply gas, which is supplied to the fuel cell, when one of the discharge gas and the supply gas is passed through the inside of the tube type hollow thread members and the other one of the discharge gas and the supply gas is passed through between the tube type hollow thread members; and a detection device which detects a generation of clogging in or between the tube type hollow thread members.
According to the above humidification system, since the detection device which is capable of detecting clogging is provided with the humidifier which humidifies the supply gas by transferring water vapor contained in the discharge gas to the supply gas by means of the water-permeable membrane that forms the bundled plurality of hollow thread members, it becomes possible to minimize the occurrence of problems, such as a decrease in the power generation efficiency of the fuel cell due to an insufficient degree of humidification of supply gas caused by the clogging in the humidifier, and avoid a failure of the fuel cell.
The above objectives may also be achieved by a humidification system for a fuel cell, wherein the detection device includes: a manometer which detects a difference in pressure of at least one of the supply gas and the discharge gas between an upper stream side and a down stream side of the humidifier; and a determination unit which determines a generation of clogging in the humidifier based on a detection signal from the manometer.
According to the above humidification system, the determination unit measures the difference in pressure of at least one of the supply gas and the discharge gas between an upper stream side and a down stream side of the humidifier based on the detection signal from the manometers and, based on the result, the generation of clogging in or between the hollow thread members in the humidifier may be easily detected. Accordingly, problems in the humidification system, such as a failure of the fuel cell, may be prevented.
The above objectives may also be achieved by a humidification system for a fuel cell, wherein the detection device includes: a dew point recorder which detects a dew point of at least one of the supply gas, which is supplied to the fuel cell, and the discharge gas, which is emitted from the fuel cell and introduced to the humidifier; and a determination unit which determines a generation of clogging in the humidifier based on a detection signal from the dew point recorder.
According to the above humidification system, the determination unit measures the dew point of at least one of the supply gas, which is introduced to the fuel cell from the humidifier, and the discharge gas, which is emitted to the humidifier from the fuel cell, based on the detection signal from the dew point recorder and, based on the result, the generation of clogging in or between the hollow thread members in the humidifier may be easily detected. Accordingly, problems in the humidification system, such as a failure of the fuel cell, may be prevented.
The above objectives may also be achieved by a humidification system for a fuel cell, wherein the detection device includes: a voltmeter which detects a voltage of the fuel cell; and a determination unit which determines a generation of clogging in the humidifier based on a detection signal from the voltmeter.
According to the above humidification system, the determination unit easily measures the output state of the fuel cell based on the detection signal from the voltmeter and, based on the result, the generation of clogging in or between the hollow thread members in the humidifier may be detected. Accordingly, problems in the humidification system, such as a failure of the fuel cell, may be prevented.
The above objectives may also be achieved by a humidification system for a fuel cell, wherein the determination unit determines if clogging is generated in or between the tube type hollow thread members by comparing the detection signal with a predetermined threshold value.
According to the above humidification system, the determination unit easily determines if clogging is generated in or between the hollow thread members by comparing the detection signal with the predetermined threshold value. Accordingly, an adverse effect to the fuel cell due to the clogging may be prevented.